Obscure props glitch, re: San Quentin 'Telechron' Clock
The electric clock shown counting down to Barbara's execution is clearly marked 'General Electric - Telechron'.
Being a clock-restorer, I'm very familiar with Telechron clocks, having serviced them. They are self-starting, unlike other (British) electric clocks which you have to start by spinning a knob or flicking a lever.
This means that a Telechron clock could show an incorrect time after a power outage, so they're fitted with an indicator that shows a red aspect if the clock has lost power. The indicator reveals that the clock may be incorrect, and has to be manually reset when the clock is corrected.
The San Quentin Telechron clock's power-fail indicator in the film clearly shows a red aspect - yet given the time-criticality of an execution, this simply wouldn't have been allowed to happen in the real prison.
Since the execution scenes were filmed on a replica studio-set, it's likely the clock was stopped and started according to the needs of the script & the director - but they forgot to reset the power-fail indicator!